In the case of an automatic transmission having a manual mode, it is necessary to provide a mechanism for preventing overspeed (over-revolution) of an engine because, differently from an automatic mode, the transmission does not automatically shift in the manual mode. Patent Document 1 discloses an automatic transmission control device with such an over-revolution prevention mechanism.
More specifically, the automatic transmission control device of Patent Document 1 has a shift pattern set for over-revolution prevention (as a forcible upshift speed change line). The control device determines the operation status of a vehicle based on a vehicle speed and a throttle opening, judges that there is applied a higher-than-allowable load when the vehicle operation status exceeds the forcible upshift speed change line, and then, performs a forcible upshift of the transmission. In the case where the vehicle is driven continuously for a predetermined time without the above forcible upshift judgment being made under the application of a load slightly lower than the allowable level, the drive system of the vehicle is overloaded so that the durability of the engine and automatic transmission deteriorates due to frictional heat of sliding parts such as bearings. In order to avoid this problem, the control device further detects a high-load operation state of the engine, measures the time of continuation of the high-load operation state and performs a forcible upshift of the transmission when the time of continuation of the high-load operation state becomes longer than or equal to a given value.